390
J. Agric. Food Chem. 1988, 36,390-392
Mani, N. V.; Ahmed, F. R.; Barnes, W. H. Acta Crystallogr. 1965, 19,693-698. Mani, N. V.; Ahmed, F. R.;-Barnes,W. H. Acta Crystallogr. 1966, 5, 375-382. McBee, E. T.; Okuhara, K.; Morton, C. J. Inorg. Chem. 1966,5,
450-457. Paudler, W. W. Nuclear Magnetic Resonance; A l l y and Bacon: Boston, MA, 1971; pp 113-117. Savant, N. K.; Medina, R.; James, A. F.; Peters, G. E. J. Agric. Food Chem. 1988, following paper in this issue. Shaw, R. A. Rec. Chem. Prog. 1967,28, 243-258. Shaw, R. A. Pure A p p l . Chem. 1975,44, 317-341.
Shaw, R. A. 2. Naturforsch. B: Anorg. Chem., Org. Chem. 1976, 31B, 641-667.
Shaw, R. A. Phosphorus Sulfur 1978, 4 , 101-121. Shaw, R. A. Pure A p p l . Chem. 1980,52, 1063-1097. Sowerby, D. B.; Audrieth, L. F. Chem. Ber. 1961,94,2670-2675. Vlek, P. L. G.; Craswell, E. T. Fert. Res. 1981, 2, 227-245. Wilson, A.; Carroll, D. F. J. Chem. SOC.1960, 2548-2552. Received for review February 28, 1986. Revised manuscript received January 5,1987. Accepted July 2,1987. This work was partially supported by the Deutsche Gesellschaft fur Technische Zusammenarbeit (GTZ) of West Germany.
Evaluation of Phenoxyaminocyclotriphosphazatrienesas Sustained-Action Soil Urease Inhibitors Narayan K. Savant,* Angela F. James, Glenn E. Peters, and Ramiro Medinal
Laboratory incubation experiments were conducted over a period of 36 days to evaluate soil urease inhibition with time a t 30 "C by the phenoxy derivatives of the phosphazene compound 2,2,4,4,6,6hexaaminocyclotriphosphazatriene. The derivatives were (1) 2-phenoxy-2,4,4,6,6-pentaaminocyclotriphosphazatriene, (2) 2,4-diphenoxy-2,4,6,6-tetraaminocyclotriphosphazatriene, and (3) 2,4,6-triphenoxy-2,4,6-triaminocyclotriphosphazatriene.After the first 16-h incubation (immediate inhibition), the monophenoxyphosphazene exhibited a 95% inhibition, whereas the triphenoxyphosphazene only inhibited 22% ; the compound phenyl phosphorodiamidate, by comparison, inhibited 100%. The immediate inhibition by the phosphazene compounds decreased with an increase in the number of phenoxy substitutions. The sustained inhibition (more than 4 days), which ranged from 40% to 95%, tended to increase with an increase in the number of phenoxy substitutions but tended to decrease with an increase in incubation temperatures from 20 to 40 "C.
Ammonia volatilization losses from broadcast urea on unsaturated soils can be serious (Terman, 1979) and can result in significantly decreased nitrogen use efficiency. One approach to increasing N use efficiency is to use urea amended with a chemical compound to retard its rapid hydrolysis (Sahrawat, 1980; Mulvaney and Bremner, 1981; Hauck, 1984). This approach has received much attention in the last 10-12 years, and several organic, inorganic, synthetic, and natural chemical compounds have been tested (Sahrawat, 1980; Mulvaney and Bremner, 1981; Liao and Raines, 1982; Martens and Bremner, 1984; Bremner and Chai, 1986). Of the compounds tested, phenyl phosphorodiamidate (PPDA) (Held et al., 1976; Martens and Bremner, 1984) and N-(mbuty1)thiophosphoric triamide (Bremner and Chai, 1986) have been reported to exhibit high soil urease inhibition. In an attempt to identify effective sustained-action urease inhibitors, Peters et al. (1988) recently synthesized and characterized three phosphazene compounds: (1) 2-phenoxy-2,4,4,6,6-pentaamin~clotriphosphazatriene (2) 2,4-diphenoxy-2,4,6,6-tetraaminocyclotriphosphazatriene, a n d (3) 2,4,6-triphenoxy-2,4,6-triaminocyclotriphosphazatriene. These compounds were in fact developed essentially for retarding hydrolysis of broadcast urea in floodwater and at the floodwater-soil interface of submerged rice soils. We International Fertilizer Development Center, P.O. Box 2040, Muscle Shoals, Alabama 35662. Present address: Lehrstuhl fur Allgemeine Chemie und Biochemie, Technische Universitat Munchen, 8050 Freising, Weihenstephan, Federal Republic of Germany. 0021-856118811436-0390$01.50/0
therefore first conducted preliminary investigations on soil urease inhibition properties of these compounds using a Crowley soil incubated under unsaturated conditions. In this paper, we reported these preliminary data on the temporal changes in soil urease inhibition by three phosphazene compounds. In separate studies conducted using several different submerged soils incubated in the greenhouse (without rice plants), we have also studied the inhibitory effects of these compounds on urea hydrolysis in floodwater and at the floodwater-soil interface, and the relevant data will be reported elsewhere. MATERIALS The three phosphazene compounds synthesized and characterized by Peters et al. (1988) were used (Table I). For comparison purposes, phenyl phosphorodiamidate supplied by ICN Pharmaceuticals (Plainview, NY) and recrystallized twice from ethanol; 2,2,4,4,6,6-hexaaminocyclotriphosphazatriene, prepared according to the procedure described by Sowerby and Audrieth (1961); and phosphoryl triamide prepared according to the procedure described by Klement and Nielsen (1960) were also included in this study (Table I). An air-dried surface soil sample (0-15 cm,
